Gordon Brown is considering doubling to 56 days the period terrorism suspects can be detained without charge.

He is expected to try to extend the 28-day limit, when he unveils his strategy on counter-terrorism.

New powers may also allow for the seizure of suspects' passports as part of plans to improve airport security.

The Tories say there is no evidence an extension on 28 days is necessary. Human rights lawyer Imran Khan said it would send "mixed messages" to Muslims.

Wednesday's announcement will be Mr Brown's first detailed statement on counter-terrorism since he became prime minister four weeks ago.

Seek consensus

An attempt to extend the period to 90 days in 2005, ended with Tony Blair's first Commons defeat as prime minister.

Mr Brown has indicated that he will seek consensus, but there is still no cross-party agreement on the issue of pre-charge detention.

Ministers say more time is needed because terrorism plots are becoming increasingly complex.

Among the options under consideration are doubling the detention time limit to 56 days and allowing judges to set a limit on a case-by-case basis.

There may also be proposals to allow authorities to remove the passports of people suspected of wanting to travel abroad for terrorism-related purposes - closing a loophole identified by police.

Mr Brown is expected to address the issue of security at ports and airports through improvements to the way passengers are monitored before they reach the UK.

'Time is right'

On Tuesday, Home Secretary Jacqui Smith said "the time is now right" to reconsider extending detention without charge beyond the current limit.

She said that the 28 day limit was already being tested.

Since the 14 day limit was extended she said one person had been charged after 15 days, four were charged after 19 and 20 days, and six were held for between 27 and 28 days, three of whom were charged.

But Mr Khan said plans to extend the limit to 56 days appeared to be a "volte face" on Mr Brown's previous announcements that he wanted to win the battle for "hearts and minds".

He told BBC Radio 4's Today programme: "It gives out the wrong signal to the community. What you are saying to the community is...we are going to batter you with legislation, we are going to arrest you, we are going to criminalise you."

Shadow Home Secretary David Davis said it would be better to change the law to allow police to continue questioning suspects after they were charged.

"The whole point of that is to relax the pressure on 28 days. If you can continue interviewing post-charge, you can charge earlier with a greater chance of conviction."

The Tories say, in a crisis, ministers already have emergency powers to extend the 28-day limit, by 30 days under the Civil Contingencies Act.

"It's not just a poker chip in the game of politics, this is about our freedoms and our security together," Mr Davis added.

MPs agreed to extend the 14-day limit on holding suspects without charge to 28 days in 2005, after rejecting the government's preferred option of 90 days.

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